The snow plow arrangement to which this invention refers fundamentally comprises a moldboard plow blade pivotally mounted to a pushframe which in turn is attached to a pushbeam mounted to the frame of the vehicle. Functionally, the pushframe is a V-shaped weldment with the moldboard frame pivotally mounted to the apex of the V and the base of the V-shaped legs pivotally secured to the pushbeam so as to permit movement of the pushframe only in a vertical direction. A cylinder, typically hydraulic, attached to the vehicle either by the pushbeam or through a separate mount and also attached typically by a chain to the pushframe raises and lowers the plow by causing the pushframe to pivot at the base of its V-shaped legs about the pushbeam. Cylinders, typically hydraulic, at each side of the V-shaped legs with one end fixed at the leg and the other end fixed to the moldboard frame provide for tilting or yaw of the board to permit the snow to be directed to one side or the other side of the plow during snow removal operation.
From a plow operation point of view, a preferred mount arrangement would be to form the base of the V-shape legs or struts on the pushframe as a box channel through which hitch pin openings are drilled in each sidewall of the channel. The channel would then be positioned between two brackets welded onto the pushframe and having openings so that the hinge pin would extend through and be journaled in the bracket and channel openings. Each strut would then have two bearing surfaces, one at each channel sidewall, which would pivot about the hinge pin which in turn is securely journaled in the two brackets which sandwich the strut end. This type of connection is preferred because it is a tight connection in the sense that there is no forward to rearward lost motion which could result in excessive wear on the connection. Also, there is no side to side lost motion while at the same time pivoting motion of the pushframe is permitted. While this type of connection is preferred in the sense of plow operation, the connection makes it difficult to attach the pushframe to the vehicle. The plow with pushframe has to be properly oriented, manually, to the vehicle and a drift or other similar implement used to bring the holes into registry. Even after the hinge pin clears or passes through the first opening in the channel sidewall, it may not easily pass through the second opening in the opposite channel sidewall. The same problems are present on removal. Thus, snow plow operators do not remove the blades during the snow plowing season even though there are many times during the season where it would be desirable to disconnect the moldboard for non-plowing vehicle use.
The prior art has recognized this problem and a number of quick connect-disconnect couplings have been proposed. The three patents cited above and incorporated herein by reference are believed typical of the various approaches. In the '369 patent, an open ended U-shaped slot in an aligning plate is used to guide the pushframe over a fixed pin and when the pin contacts the end of the slot, a latch having a similar open ended U-shaped slot is pivoted over the pin so that the pin is locked between the two U-shaped slots which are at right angles to one another. A similar arrangement is shown in the '008 patent in that the U-shaped slot in the aligning plate of the '369 patent is replaced by a V-shaped slot in the '008 patent to improve the gathering range of the connection. When the pin is positioned at the base of the V-shaped slot of the aligning plate in the '008 patent, a similar open ended latch is pivoted over the hinge pin so that the pin is held between the latch and the aligning plate as done in the '369 patent. In the '008 patent, the opening in the V-shaped aligning plate is at right angles to the opening in the latch and is identified in function to the arrangement disclosed in the '369 patent. A similar arrangement is also disclosed in the '562 patent which uses a bell crank arrangement positioned on the pushframe to pivot a J-shaped hook into locking engagement with the hinge pin after the aligning plate on the coupling has positioned the frame into proper relationship with the pin. While all three patents have a quick connect-disconnect coupling, the pin connection function they provide is poor. In essence, the pin is captured or journaled between two plates which must have openings extending at least 180.degree.. This means the pin is not journaled about its entire circumference resulting in a connection which inherently has to have more looseness or slop, at least when compared to the prior art pin connection which did not have quick connect features. In addition, each of the patents discussed journal the hinge pin at only one point per strut. This arrangement is thus less stable and more susceptible to wear than the prior art arrangement discussed above which did not have quick disconnect-connect features. Finally, all arrangements use permanently mounted or fixed hitch pins or hitch rods which makes their replacement difficult and/or expensive.